HANDLING 16/07
EXPLAINED SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
How does the spring rate affect the steering? Can the shock absorber rate reduce the body roll? Why does increasing the rate of the rear sway bar induce more over steer? These are just a few of the questions we will examine in this TechStop on handling. But first, we should ask, “What is handling?” The technical definition of handling is generally accepted as, “the amount and percentage of traction each wheel and tyre has verses the feel to the driver of the car”. Even this technical definition allows room for different opinions on how well a car handles because of differing characteristics of the car. A car must supply feel to the driver, and the most important element of handling is how well the tyres perform, remembering that in real terms the “foot print’ of the tyre is not that big and it relies on how well the car is “set-up”. The ability of the tyres to maintain their grip is greatly influenced on the type, size and compound. If the car is fitted with the appropriate tyre for the intended use, fitted to the corresponding rims and the correct tyre pressure has been applied , then the car has good start to achieving the desired result. Handling is all
encompassing, Acceleration, Braking and Cornering. For a car to achieve its true potential, all three of requirements must have the ability to come together. However the tyres will only work to their maximum effect if the steering and suspension allow them to. This is where we start to discuss the importance of dynamic geometry. Though the wheel alignment geometry is adjusted while the vehicle is stationary, (static) it is important to note that it is for when the car is in motion (dynamic). Just about all the wheel angles alter when the car is in motion, this is where the suspension rate becomes active, you can have the best tyres money can buy, have the best wheel alignment performed on the car, but if the suspension is not right the car will not perform. The dynamic changes of the geometry is effected by a number of factors, these including the general condition of the chassis and suspension, the static alignment angles, spring rates, shock absorber rates, sway bar rates and the balance of the car (corner weights and centre of gravity). This TechStop will examine how individual components impact on the overall package of a good handling car.
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HANDLING 16/07
EXPLAINED
As we have touched on the importance of tyres and wheel alignment, the other major handling components SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS of chassis tuning are: AND WHEEL ALIGNMENT SPECIALISTS Springs, Shock absorbers , Anti sway bars (often called sway bars) and bushes As we have touched on the importance of tyres and Shock Absorbers Springs: wheel alignment, the other major handling components Shock dotwo notbasic absorb shocks, they control the Springs, whetherShock they are Coil, Leaf, Torsion Bars or Airabsorbers Bags, serve of chassis tuning are: Springs, absorbers , Anti oscillations of the suspension The stiffer the Firstbars) and foremost they take care of holding up the sprung weight of themovement, car, sway bars (oftenfunctions. called sway and bushes spring the stiffer the shock. obviously if there were no springs the car would sit on the bump stops and that does NOT Springs make for good handling. The second one is to provide resistance the movement of the They do this bytocontrolling the compression and the mass, vertically, pitch and roll. The velocity of this movement is controlled by the shock rebounding of the suspension as the car travels over Springs, whether they are Coil, Leaf, Torsion Bars or absorbers. The springs and shock absorbers are aamatched set-up, make a choice given surface. Also they will on have an effect on the Air Bags, serve two basic functions. First and foremost springs first, then select the shocks that are best suited to obtain maximum control. energy created associated with suspension travelling they take care of holding up the sprung weight of the The spring has many functions, like: laterally created by cornering and longitudinal, created car, obviously if there were no springs the car would sit • Controlling dynamic Camber setting by accelerating and braking. on the bump stops and that does NOT make for good • The Ride Height, which effects the car’s Centre of Gravity and Roll Centres handling. The second one is to provide resistance to damping, magnitude • The Roll Stiffness, which is the resistanceWithout for the body to rollthe when corneringof the suspension the movement of the mass, vertically, pitch and roll. The movement would never stop increasing. In terms of velocity of this movement controlled by the shock for theenergy, To calculateiswhat Spring Rate is required car the following is required: damping data absorbs most of the energy the absorbers. The springs and shock absorbers are a • Sprung weight of the car at each corner car receives as it moves, unlike springs, that store matched set-up, make a choice on springs first, then the energy and then releases it. Imagine a car with • Weight distribution , front to rear select the shocks that are best suited to obtain maximum no damping effect or the wrong valving in the shock • Motion Ratio of the spring platform control. The subsequent impacts from the undulations • Wheel Rate(Calculated spring rate at the absorber. wheel) on the tyres would make the suspension uncontrollable, The spring has many like:as mounted in the car • functions, Spring Angle, which is not a good thing. Dampers absorb • The compound of the tyres • Controlling dynamic Camber setting. all the excess energy and allow the tyres to stay in contact with the road surface as • The Ride Height, which effects the car’s Centre of Shock Absorbers: much as possible. Gravity and Roll Centres. Shock absorbers do not absorb shocks, they control the oscillations of the suspension This also indicates that the damping rate • The Roll Stiffness, which The is the resistance forthe thestiffer bodythe shock. movement, stiffer the spring always be matched to the to roll when cornering. They do this by controlling the compression and should the rebounding of the suspension as spring the car rate. travels overRate a given surface. for Also they To calculate what Spring is required the carwill thehave an effect on the energy created associated suspension travelling laterally created by cornering anddamping longitudinal, createdthe by speed at Note: the only alters following data iswith required: accelerating and braking. which the roll and pitching motions occur, wheel alignment, the other major handling components • Sprung weightWithout of the car at each damping, thecorner. magnitude of the suspension movement would never stopSo increasing. it does not alter their extent. if you want In terms of energy, damping absorbs most of the energy the car receives as it moves, unlike • Weight distribution, front to rear. the vehicle to roll less, adjust the Anti-Roll led sway bars) and bushes springs, that store the energy and then releases it.bars Imagine a car with no damping effect or change the spring rate, leaveorthe • Motion Ratio of spring platform. thethe wrong valving in the shock absorber. The subsequent impacts from the undulations on shocks last. the tyres would make the suspension uncontrollably, which is not a good thing. Dampers • Wheel Rate(Calculated spring absorb all the excess energy and allow the tyres to stay in contact with road surface as How to select thetheshock absorber r Air Bags,rate serve two basic at the wheel). much as possible. ng up the • sprung weightas ofmounted the car, in that the damping rate should always • Check suspension travel,rate. the shock Spring Angle,This also indicates be the matched to the spring on the bumpthestops and that does NOT must have the correct opened car. Note: the damping only alters the speed at which the roll and pitching motions occur,and it does de resistance to the movement theextent. So if you want the vehicle to closed not alter of their roll less,length. adjust the Anti-Roll bars or • The compound of the tyres. spring rate, leave the shocks last. movement is controlled change by thethe shock • Take into account the “Motion Ratio”
atched set-up, make a choice on How to select the shock absorber: ed to obtain maximum control.
when selecting the valve code.
• The angle that the shockand absorber Check the suspension travel, the shock must have the correct opened closed is mounted will also affect the valve rate. length • Take into account the “Motion Ratio” when valve code • Tselecting he shockthe absorber valve code is to be • The angle that the shock absorber is mounted will also affect the valve rate. ntre of Gravity and Roll Centres matched to the spring rate. • The shock absorber valve code is to be matched to the spring rate r the body to roll when cornering •
the following data is required:
eel)
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laterally. If one side of the suspension is compressed, one end of the bar is lifted. The other end will also want to go up, and in turn pulling the other side of the suspension up also, basically creating more resistance to body roll. This effect is controlled by the torsional strength of the bar, smaller diameter less resistance, larger the bar, the greater the resistance. When both sides are moving equally, down when the car is braking or up when the car is accelerating, the bar has no effect on the suspension. Anti- Roll Bars only effect the lateral balance of the16/07 car, not the longitudinal balance. • Anti-Roll Bars aren’t the only things that effect the car’s roll stiffness, they work in conjunction with the springs and shocks. SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS • Stiffer in the front and softer in the rear, promotes understeer. flexible flat-side-on position on other systems. This lets • Softer in the front and stiffer in the rear promotes oversteer. Anti-Sway Bars a mechanic tunewhen the rollgoing stiffness different situations • Anti –Sway will“sideways restrict suspension travel, of this offfor road with your Anti-sway barsBars are like springs, they work so be mindful without replacing the entire bar. 4laterally. W.D. If one side of the suspension is compressed, Some anti-roll intended foralso racing, are one endbars, of theparticularly bar is lifted. those The other end will want to go up, and in turn pulling other side of thesome externally adjustable while the car is inthethe pit whereas up also,inbasically creating resistance to systemssuspension can be adjusted real time by themore driver from inside body roll. the car. This allows the stiffness to be altered, for example by Thisor effect is controlled by the of some the increasing reducing the length oftorsional the leverstrength arms on diameter resistance, larger the bar, the systems,bar, or smaller by rotating a flatless lever arm from a stiff edge-on greater the resistance. position to a more flexible flat-side-on position on other are moving whenfor thedifferent systems.When Thisboth lets sides a mechanic tuneequally, the rolldown stiffness car is braking or up when the car is accelerating, the situations without replacing the entire bar.
HANDLING
EXPLAINED
bar has no effect on the suspension. Anti- Roll Bars only effect the lateral balance of the car, not the longitudinal Suspension Bushes: balance.
Bushes Suspension bushes are one of the most poorly understood and Suspension undervalued components of a car’s overall ngs, they work Suspension bushes are one of the most poorly handling. It can be easy to discount the role that such an inconsequential looking piece of rubber can play in s compressed, understood and undervalued components of looks a car’s the proper operation of a car’s suspension system. This is a huge mistake. Although a suspension bush nd will also overall handling. It can be easy to discount the role simple, ther side of it is quite a complex component that fulfills a variety of important roles and if they become worn or that such an inconsequential looking piece of rubber ngdamaged more you will notice a variety of adverse effects. can play in the proper operation of a car’s suspension The following are some of the classic symptoms: system. This is a huge mistake. Although a suspension l strength of • Excessive road noise bush looks simple, it is quite a complex component that e, larger the fulfills a variety of important roles and if they become • Poor steering response worn or damaged you will notice a variety of adverse own when • the Poor handling (Over or Understeer characteristics) effects. elerating, the bar has no effect on the suspension. Anti- Roll Bars • Inaccurate wheel alignment • Anti-Roll Bars aren’t the only things that effect the car’s , not the longitudinal balance. roll stiffness, they work conjunctionofwith springs • effect Not obtaining fullinthe thethe tyre foot print The following are some of the classic symptoms: hings that the car’s rollthe stiffness, theyeffects work in conjunction and shocks. Excessive road noise. The use of different types of materials for the bushes, do have • their the rear, promotes advantage: • Stifferundersteer. in the front and softer in the rear, promotes • Poor steering response. the rear• promotes oversteer. understeer. A high capacity to bear tension • Poor handling (Over or Understeer characteristics). spension travel, so be mindful of this when going off road with your • Assist precise wheelinalignments • Softerininmore the front and stiffer the rear promotes • Inaccurate wheel alignment. oversteer. • forThe carare becoming more reactive ntended racing, • Not obtaining the full the effects of the tyre foot print. the pit•whereas some Increase roadBars holding • Anti –Sway will restrict suspension travel, so be
the driver from insideof this when going off road with your 4 W.D. mindful The use of different types of materials for the bushes, do ltered, for example by have bolts their advantage: When installing any suspension bushes, only tighten the mounting finger tight. Do not proceed until anti-roll bars, particularly those intended for lever armsSome on some theacar’s weight resting on the wheels and at natural Then fully tighten the bolts to areisexternally adjustable while thethe carcar is inisthe from stiffracing, edge-on • Aride highheight. capacity to bear tension. whereas torque. some systems can be adjusted in real time position on pit other the recommended This procedure will prevent premature wear of the bushes caused by increased • Assist in more precise wheel alignments. the driver from car.ride Thisheight allows the rolltorsional stiffnessbyfor different stress placed oninside them.theThe maystiffness also be affected if this process is not followed. bar. to be altered, for example by increasing or reducing the • The car becoming more reactive. length of the lever arms on some systems, or by rotating • Increase road holding. a flat lever arm from a stiff edge-on position to a more
poorly understood and undervalued components of a car’s overall role that such an inconsequential looking piece of rubber can play in on system. This is a huge mistake. Although a suspension bush looks t that fulfills a variety of important roles and if they become worn or verse effects. ymptoms:
Straight advice, specialists you understand and...
HANDLING 16/07
EXPLAINED SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
When installing any suspension bushes, only tighten the mounting bolts finger tight. Do not proceed until the car’s weight is resting on the wheels and the car is at natural ride height. Then fully tighten the bolts to the recommended torque. This procedure will prevent premature wear of the bushes caused by increased torsional stress placed on them. The ride height may also be affected if this process is not followed.
Although bump-steer is predominantly a front end geometry problem, certain suspension systems can produce similar problems on the rear of a car, for instance fully independent suspension systems. In general, most high technology cars, have very little bump-steer. The accuracy of the design and build process on these cars ensures the geometrical accuracy.
Measuring bump-steer is simply a case of measuring the deviation a wheel takes when the suspension is compressed. Very accurate instruments such as a modern four wheel alignment machine can measure Bump Steer: deviation as little as one mm. Changing the vertical position of the steering rack or rod-end pivots will Bump steer is the toe-in or toe-out of the front wheels as the the bump-steer suspension readings. goes from normal ride height change
through full bump (suspension system moves up) to full droop (suspension system moves down). Causes of Bump Steer: Measurement is usually limited to 75mm up and 75mm down from ride height. It is specified either by a graph or measurements at 25mm, 50mm and 75mm. • Steering Rack not level. • Drag link not level.
So, what does bump-steer do to a car’s handling? There are a number of possibilities, depending on the • Different length Ackerman arms. severity of the problem in, including: • Direction change under braking • Different height or angle of the Ackerman arms. • Shake in the steering system (particularly at the steering wheel) • Tie rod and L.C.A. angles do not intersect. Bump Steer • Sudden loss of grip during any part of the cornering process (entry, middle, or exit) Height steering caror pulls to one at certain points on• the trackof(can be ongear. straights too) Bump steer is• theThe toe-in toe-out of side the front wheels All of the above are directly to suspension at a time when the components. driver did not input any as the suspension goes from normal related ride height through movement • Bent or misaligned steering steering angle change. full bump (suspension system moves up) to full droop (suspension system moves down). Measurement is is predominantly a front usuallyAlthough limited to bump-steer 75mm up and 75mm down from ride end height.geometry It is specified eithercertain by a graph or measurements problem, suspension systems can at 25mm, 50mmsimilar and 75mm. produce problems on the rear of a car, for
instance fully independent systems. So, what does bump-steer do to asuspension car’s handling? There are a number of possibilities, depending on the severity In general, most high technology cars, have very of the problem in, including: little bump-steer. The accuracy of the design and
• Direction braking. buildchange processunder on these cars ensures the geometrical accuracy. • Shake in the steering system (particularly at the steering wheel).
Measuring bump-steer is simply a case of measuring the deviation a wheel takes when the suspension is
• Sudden loss of grip during any part of the cornering compressed. Very accurate instruments such as a modern four wheel alignment machine can measure process (entry, middle, or exit).
deviation as little as one mm. Changing the vertical position of the steering rack or rod-end pivots will
• The car pullsthe to one side at certain points on the track change bump-steer readings. (can be on straights too).
Causes ofare Bump Steer: All of the above directly related to suspension Steering not level movement at•a time whenRack the driver did not input any • Drag link not level steering angle change. • • • • •
Different length Ackerman arms Different height or angle of the Ackerman arms Tie rod and L.C.A. angles do not intersect Height of steering gear Bent or misaligned steering components
Straight advice, specialists you understand and...
HANDLING 16/07
EXPLAINED SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
Wheel Alignment The final operation of any modification, alteration or set up is the wheel alignment, why? • Directional stability. • Obtain maximum affect from the tyres. • Stable braking. A poor or no wheel alignment will result in a vehicle that will be lacking in the appropriate responses.
The tyre foot print is quite small in the scheme of things, it is all very well in having an engine that is developing good reliable horse power, but if the car can’t put it on to theupground, then you are wasting your time. ation or set is the wheel alignment, why?
s
Not all cars and drivers like the same settings, as there are too many variables. • The balance of the car.
• The weight of the driver. vehicle that will be lacking in the appropriate responses. • The heme of things, driving it is allstyle. very well in having an engine that is the car can’t puttyre it on to the ground, then you are wasting your • The pressures.
If you are using your car for competition, make sure you set the geometry up for the car to suit the circuit. The toe setting will vary enormously from circuit to circuit. Is it short tight and twisty or open and fast. These are the considerations to be taken into account when setting up the vehicle. A tyre temperature gauge is very handy as well. After a test session check the temperature across the foot print of the tyre, to see if there are any major variations and if there are alter the geometry to have a uniform temperature pattern across the tyre.
Pedders Wheel Alignment products Pedders suspension have available an extensive range of aftermarket wheel alignment products. So now there is no need to put up with “close enough is good enough” In the Pedders range, there are Eccentric Bushes, Eccentric Pivot Bearings, Camber Pins, Shim Replacement Kits and Adjustable front Radius Arm Bushes.
• The type/compound of tyres.
s, as there are too many variables.
When conducting the wheel alignment, it is very important to have the car at it’s usual operating weight. All fluids, including fuel, oils, washer bottle, driver drink bottle etc., must be at their desired level. Tyre pressures correct, drivers weight, including clothing and helmet, is to be in the car.
is very operating er bottle, ed level. ncluding
make sure e circuit. circuit to and fast. account
well. After a test session check the temperature across the foot variations and if there are alter the geometry to have a uniform
Straight advice, specialists you understand and...
HANDLING 16/07
EXPLAINED SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
Handy Hints Component
Reduce Under-steer
Reduce Over-steer
Weight distribution
C. of G. towards rear
C. of G. towards front
Front shock dampers
Softer
Stiffer
Rear shock absorber
Stiffer
Softer
Front sway bar
Softer
Stiffer
Rear sway bar
Stiffer
Softer
Front tyre selection¹
Larger contact area
Smaller contact area
Rear tyre selection
Smaller contact area
Larger contact area²
Front wheel rim width or diameter
Larger²
Smaller
Rear wheel rim width or diameter
Smaller
Larger²
Front tyre pressure
Lower pressure
Higher pressure
Rear tyre pressure
Higher pressure
Lower pressure
Front wheel camber
Increase negative camber
Reduce negative camber
Rear wheel camber
Reduce negative camber
Increase negative camber
Rear spoiler
Smaller
Larger
Front height (because these usually affect camber and roll resistance)
Lower front end
Raise front end
Rear height
Raise rear end
Lower rear end
Front in
Decrease
Increase
Rear toe in
Decrease
Increase
1) Tyre contact area can be increased by using wider tyres, or tyres with fewer grooves in the tread pattern. Of course fewer grooves has the opposite effect in wet weather or other poor road conditions. 2) These also improve road holding, under most conditions.
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